There are known compounds of the general formula ##STR3## from German Pat. No. 1,493,574. In this formula R.sub.1, R.sub.2 and R.sub.3 are the same or different and are hydrogen or a hydroxy group, a methoxy group or chlorine. R.sub.4 is hydrogen or a methyl or ethyl group. R.sub.5 is hydrogen or a methyl group. R.sub.6 is hydrogen or a hydroxy group. R.sub.7 and R.sub.8 are the same or different and are a methyl group, a methoxy group or chlorine.
These compounds are pharmacodynamically active and particularly improve the heart function.